JP2021185626A - Electrode for aluminum electrolytic capacitor - Google Patents

Abstract

To provide an electrode for an aluminum electrolytic capacitor which can improve the water resistance of a chemical conversion film with a withstand voltage of 400 V or more.SOLUTION: A hydration step of bringing an aluminum electrode into contact with a hydration treatment solution having temperature of 78°C to 92°C to form a hydration film on the aluminum electrode, and a chemical conversion step of performing chemical conversion at a chemical conversion voltage of 400 V or higher in a chemical conversion liquid having temperature of 58°C to 78°C to form a chemical conversion film on an aluminum electrode are executed to manufacture an electrode for an aluminum electrolytic capacitor. At that time, the amount of the hydrated film is optimized. In such electrode for the aluminum electrolytic capacitor, the number of pores exposed on the cut surface when the chemical conversion film is cut is 150/μm2 or less, such that the water resistance is high.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrode for an aluminum electrolytic capacitor in which a chemical conversion film is formed on an aluminum electrode.

In the manufacturing process of an anode foil for an aluminum electrolytic capacitor, an aluminum electrode having a porous layer is immersed in a hydration treatment solution such as high-temperature pure water to form a hydrated film on the surface of the aluminum electrode (hydration step). , Chemical formation is carried out in a chemical conversion solution containing an organic acid, an inorganic acid and a salt thereof (chemical conversion step), and a chemical conversion film made of aluminum oxide is formed on the surface. By forming a hydrated film before the chemical conversion step, the amount of electricity required for chemical conversion can be reduced and the capacitance per unit area can be improved (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2014-57000

In the chemical conversion film formed when the chemical conversion is performed at a chemical conversion voltage of 400 V or more after the hydration step, there are many defects consisting of pores having a diameter of several nm to several tens of nm. It is believed that this occurs because the hydrated film undergoes volume shrinkage as it dehydrates and changes to aluminum oxide. The chemical conversion film in which these defects are present has a drawback that the chemical conversion film is liable to be hydrated and deteriorated because water easily infiltrates from the surface.

As a result of various studies by the present inventors regarding such defects, when the chemical formation is performed after the hydration step, the defects start to occur from a voltage of 300 V or more, especially at 400 V or more, further 500 V or more. I found it to be noticeable. Further, as a result of repeating experiments and discussions, the present inventors, in the case of chemical conversion at a voltage of 300 V or less, even if the defect occurs, the chemical conversion liquid or water permeates the defect in the chemical conversion step. , The defect is regenerated and repaired. However, when chemicals are formed at a voltage of 400 V or higher, the heat generated by the chemical conversion film is enormous, so that the chemical conversion liquid or water boils on the surface of the film before the chemical conversion liquid or water permeates the defects in the chemical conversion process. It was found that it was difficult to repair the defect because it evaporated.

In view of the above problems, an object of the present invention is to provide an electrode for an aluminum electrolytic capacitor capable of improving the water resistance of a chemical conversion film having a withstand voltage of 400 V or more.

In order to solve the above problems, the present invention is an electrode for an aluminum electrolytic capacitor in which a chemical conversion film having a withstand voltage of 400 V or more is formed on an aluminum electrode, and the empty surface exposed on the cut surface when the chemical conversion film is cut. It is characterized in that the number of holes is 150 / μm ^{2 or less.}
Further, another aspect of the present invention is an electrode for an aluminum electrolytic capacitor in which a chemical conversion film having a withstand voltage of 400 V or more is formed on an aluminum electrode, and the cut surface when the chemical conversion film is cut is observed by FE-SEM. The feature is that the number of pores existing inside the chemical conversion film exposed on the cut surface is 150 / μm ^{2 or less.}

In the present invention, the number of pores (defects) exposed on the cut surface when the chemical conversion film is cut is 150 /
It is μm ² or less, and there are few defects in the chemical conversion film. Therefore, since water does not easily infiltrate from the surface of the chemical conversion film, the chemical conversion film does not easily deteriorate due to hydration, and the water resistance of the chemical conversion film can be improved.

In the present invention, the number of the pores ^{is preferably 100 / μm 2} or less.
In the present invention, the aluminum electrode can adopt an embodiment made of an etched foil obtained by etching an aluminum foil.
In this case, the number of pores existing inside the chemical conversion film exposed on the cut surface when the chemical conversion film is cut so as to cross the tunnel-shaped pit generated by etching is 150 / μm ² or less.
In the present invention, the aluminum electrode may be an embodiment in which a porous layer made by sintering aluminum powder is laminated.
In this case, the number of pores existing inside the chemical conversion film exposed on the cut surface when the chemical conversion film is cut so as to cross the porous layer is 150 / μm ² or less.

In the method for manufacturing an electrode for an aluminum electrolytic capacitor according to the present invention, a hydration step of bringing the aluminum electrode into contact with a hydration treatment liquid having a temperature of 78 ° C to 92 ° C to form a hydration film on the aluminum electrode, and a temperature. The aluminum electrode has a chemical conversion step of forming a chemical conversion film on the aluminum electrode by performing chemical conversion in a chemical conversion liquid from 58 ° C. to 78 ° C. at a chemical conversion voltage of 400 V or more. When the ratio to the mass before the hydration step is xwt%, the film withstand voltage Vf (V) and the ratio xwt% are the following conditional equations (0.01 × Vf) ≦ x ≦ (0.017 × Vf + 28).
It is characterized by satisfying.

In the method for manufacturing an electrode for an aluminum electrolytic capacitor according to the present invention, the hydration step is carried out at a relatively low temperature of 78 ° C. to 92 ° C. based on the finding that water contained in the hydration film is easily desorbed at 60 ° C. to 90 ° C. Perform at ° C. Therefore, the water in the hydrated film is difficult to be removed, and a hydrated film having a large amount of water is formed. Therefore, even if defects (pores) occur due to volume shrinkage when the hydrated film is dehydrated and changed to aluminum oxide in the chemical conversion process, sufficient water is present in the chemical conversion film, so that the chemical conversion process Can effectively repair defects in. Further, in the chemical conversion step, the temperature of the chemical conversion liquid is changed from 58 ° C. to 78 ° C., so that it is difficult for water to be separated from the hydrated film in the hydration step. Therefore, since sufficient water is present in the hydrated film even during the chemical conversion, defects can be effectively repaired in the chemical conversion step. Therefore, since the number of pores (defects) exposed on the cut surface when the chemical conversion film is cut ^{can be reduced to 150 / μm 2} or less, it is difficult for water to infiltrate from the surface of the chemical conversion film. Therefore, the chemical conversion film is less likely to be hydrated and deteriorated, and the water resistance of the chemical conversion film can be improved.

Further, in the present invention, the amount of the hydration film formed in the hydration step is appropriate. That is, if the amount of the hydration film formed in the hydration step is too small, the heat generated during the chemical conversion becomes large, so that it becomes difficult to proceed with the repair of defects in the chemical conversion step. On the other hand, if the amount of the hydrated film formed in the hydration step is too large, the thickly formed hydrated film prevents the chemical conversion liquid or water from penetrating the defect, which hinders the repair of the defect. Be done. Therefore, according to the present invention, the number of pores (defects) exposed on the cut surface when the chemical conversion film is cut ^{can be reduced to 150 / μm 2} or less, so that water infiltrates from the surface of the chemical conversion film. It's hard to do. Therefore, the chemical conversion film is less likely to be hydrated and deteriorated, and the water resistance of the chemical conversion film can be improved. It should be noted that the defects can be removed to some extent by performing rechemicalization after depolarization in the chemical conversion step, but cannot be sufficiently removed at a chemical conversion voltage of 400 V or higher. This is because the chemical conversion film is thickly formed, and even if depolarization is performed, defects inside the film are left behind.

In the present invention, in the chemical conversion step, the moving speed of the aluminum electrode is represented by a three-dimensional velocity vector A, and the chemical formation is in a range of 10 cm in a direction perpendicular to the surface of the aluminum electrode from the surface of the aluminum electrode. The average velocity of the liquid is represented by a three-dimensional velocity vector B, the relative velocity of the chemical conversion liquid to the aluminum electrode is represented by a three-dimensional velocity vector BA, and the absolute value of the velocity vector BA is | BA. When expressed as |
The absolute value | BA | of the velocity vector is the following conditional expression 3 cm / s ≦ | BA | ≦ 100 cm / s.
It is preferable to satisfy. According to such a configuration, since the relative velocity of the chemical conversion liquid to the surface of the aluminum electrode is appropriate, the heat generated from the aluminum electrode during chemical conversion can be efficiently dissipated into the chemical conversion liquid. Therefore, even if the chemical conversion voltage is 400 V or more, in the chemical conversion step, the chemical conversion liquid or water can permeate the defects in the chemical conversion film, so that the defects are repaired. Therefore, since the capacitance is high and there are few defects in the chemical conversion film, the chemical conversion film is less likely to be hydrated and deteriorated. Here, when | BA | is less than 3 cm / s, the chemical conversion film cannot sufficiently dissipate heat from the surface of the aluminum electrode and the diffusion of ions becomes insufficient. The defects inside are not sufficiently repaired, the leakage current is high, and the electrodes for aluminum electrolytic capacitors are prone to hydration deterioration. On the other hand, when | BA | exceeds 100 cm / s, the capacitance tends to decrease because the elution of aluminum ions from the surface of the aluminum electrode becomes excessive.

In the present invention, the absolute value | BA | of the velocity vector is the following conditional expression 5 cm / s ≦ | BA | ≦ 30 cm / s.
It is preferable to satisfy.

In the present invention, when the absolute values of the velocity vectors A and B are expressed as | A | and | B |, respectively,
The absolute values | A | and | B | of the velocity vector are the following conditional expressions 0 cm / s ≦ | A | ≦ 100 cm / s, respectively.
3 cm / s ≦ | B | ≦ 100 cm / s
It is preferable to satisfy.

In the electrode for an aluminum electrolytic capacitor according to the present invention, the number of pores (defects) exposed on the cut surface when the chemical conversion film is cut is 150 pieces / μm ² or less, and there are few defects in the chemical conversion film. Therefore, since water does not easily infiltrate from the surface of the chemical conversion film, the chemical conversion film does not easily deteriorate due to hydration, and the water resistance of the chemical conversion film can be improved. Further, in the method for manufacturing an electrode for an aluminum electrolytic capacitor according to the present invention, the hydration step is carried out from a relatively low temperature of 78 ° C. based on the finding that water contained in the hydration film is easily desorbed at 60 ° C. to 90 ° C. Perform at 92 ° C. Therefore, the water in the hydrated film is difficult to be removed, and a hydrated film having a large amount of water is formed. Further, in the chemical conversion step, the temperature of the chemical conversion liquid is changed from 58 ° C. to 78 ° C., so that it is difficult for water to be separated from the hydrated film in the hydration step. Therefore, since sufficient water is present in the hydrated film, defects can be effectively repaired in the chemical conversion step. In addition, the amount of the hydration film formed in the hydration step is appropriate. Therefore, since the number of pores (defects) exposed on the cut surface when the chemical conversion film is cut ^{can be reduced to 150 / μm 2} or less, it is difficult for water to infiltrate from the surface of the chemical conversion film. Therefore, the chemical conversion film is less likely to be hydrated and deteriorated, and the water resistance of the chemical conversion film can be improved.

It is explanatory drawing which shows the inspection method of the hole (defect) in the chemical conversion film of the electrode for an aluminum electrolytic capacitor. It is explanatory drawing of the hole (defect) in the chemical conversion film of the electrode for an aluminum electrolytic capacitor. It is a graph which shows the appropriate range of the amount of the hydration film generated in the hydration step in the manufacturing method of the electrode for an aluminum electrolytic capacitor to which this invention is applied. It is explanatory drawing which shows schematically the chemical formation process of the electrode for an aluminum electrolytic capacitor to which this invention is applied.

(Electrodes for aluminum electrolytic capacitors)
In the present invention, in manufacturing an electrode for an aluminum electrolytic capacitor, the surface of the aluminum electrode is chemically formed to manufacture an electrode for an aluminum electrolytic capacitor. As the aluminum electrode, an etched foil obtained by etching an aluminum foil, a porous aluminum electrode in which a porous layer formed by sintering aluminum powder is laminated on both sides of an aluminum core material, or the like can be used. The etched foil comprises a porous layer in which tunnel-like pits are formed. In the porous aluminum electrode, for example, a porous layer 30 having a thickness of 150 μm to 3000 μm is formed on each of both surfaces of an aluminum core material having a thickness of 10 μm to 50 μm. The porous layer is a layer obtained by sintering aluminum powder, and the aluminum powder is sintered while maintaining voids with each other.

(Construction of aluminum electrolytic capacitor)
In order to manufacture an aluminum electrolytic capacitor using a chemicalized aluminum electrode (electrode for an aluminum electrolytic capacitor), for example, an anode foil made of a chemicalized aluminum electrode (electrode for an aluminum electrolytic capacitor) and a cathode foil are separated from each other. A condenser element is formed by interposing and winding it. Next, the capacitor element is impregnated with the electrolytic solution (paste). After that, the capacitor element containing the electrolytic solution is housed in the outer case, and the case is sealed with the sealing body. If the water resistance of the chemical conversion film is low in the aluminum electrolytic capacitor having such a configuration, the chemical conversion film may be deteriorated by the moisture in the air while the electrode for the aluminum electrolytic capacitor is stored, and the characteristics of the aluminum electrolytic capacitor may be deteriorated. Further, if the chemical conversion film is deteriorated by the moisture in the electrolytic solution after the aluminum electrolytic capacitor is manufactured, the reliability of the aluminum electrolytic capacitor is lowered. Therefore, the electrodes for aluminum electrolytic capacitors are required to have high water resistance.

When a solid electrolyte is used instead of the electrolytic solution, a solid electrolyte layer is formed on the surface of an anode foil made of a chemicalized aluminum electrode (electrode for an aluminum electrolytic capacitor), and then a cathode layer is formed on the surface of the solid electrolyte layer. After that, the exterior is made of resin or the like. At that time, an anode terminal electrically connected to the anode and a cathode terminal electrically connected to the cathode layer are provided. In this case, a plurality of anode foils may be laminated. In the aluminum electrolytic capacitor having such a configuration, if the water resistance of the electrode for the aluminum electrolytic capacitor is low, the chemical conversion film is deteriorated by the moisture invading through the exterior such as resin, so that the electrode for the aluminum electrolytic capacitor has high water resistance. Required.

(Electrodes for aluminum electrolytic capacitors)
FIG. 1 is an explanatory diagram showing a method of inspecting holes (defects) in a chemical conversion film of an electrode for an aluminum electrolytic capacitor. FIG. 2 is an explanatory diagram of holes (defects) in the chemical conversion film of the electrode for an aluminum electrolytic capacitor. In addition, FIG. 2 shows a photograph of a cross section of a chemical conversion film having many pores observed by FE-SEM so that the existence of pores can be easily understood.

In the electrode for an aluminum electrolytic capacitor, if there are many pores (defects) in the chemical conversion film, water easily infiltrates from the surface, so that the chemical conversion film tends to be hydrated and deteriorated. Therefore, the smaller the number of defects in the chemical conversion film, the higher the water resistance of the electrode for the aluminum electrolytic capacitor. Therefore, in this embodiment, as described with reference to FIGS. 1 and 2, the number of pores in the chemical conversion film is controlled to a predetermined value or less. More specifically, by controlling the number of pores exposed on the cut surface to a predetermined value or less when the chemical conversion film of the electrode for an aluminum electrolytic capacitor is cut, the number of pores in the chemical conversion film is reduced to a predetermined value or less. To control.

FIGS. 1A and 2 show a case where the chemical conversion film is cut along the surface of the electrode for an aluminum electrolytic capacitor having a chemical conversion film formed on the etched foil, and the tunnel-shaped pit is black. Shown as an area. In addition, there is a chemical conversion film around the pit. Further, as shown in FIG. 2, since the pores (defects) are exposed on the cut surface of the chemical conversion film, the number of pores per ^{1 μm 2 can be measured.}

As shown in FIG. 1 (b), the chemical conversion film may be cut along the pits. In this case as well, since pores (defects) are exposed on the cut surface of the chemical conversion film, per ^{1 μm 2.} The number of vacancies can be measured.

In this embodiment, the number of pores exposed on the cut surface when the chemical conversion film of the electrode for an aluminum electrolytic capacitor is cut is set to ^{150 / μm 2 or less.} Therefore, there are few defects in the chemical conversion film. Therefore, since water does not easily infiltrate from the surface of the chemical conversion film, hydration deterioration does not occur easily and water resistance is high. The number of pores ^{is more preferably 100 / μm 2} or less, and according to such an embodiment, the water resistance of the electrode for an aluminum electrolytic capacitor can be significantly improved.

(Manufacturing method of electrodes for aluminum electrolytic capacitors)
In the method for manufacturing an electrode for an aluminum electrolytic capacitor of this embodiment, a hydration step of contacting the aluminum electrode with a hydration treatment solution such as pure water to form a hydrated film on the aluminum electrode, and a chemical conversion of 400 V or more in the chemical conversion solution. A chemical conversion step is performed in which the aluminum electrode is formed with a voltage and a chemical conversion film is formed on the aluminum electrode. In the present embodiment, in the hydration step, an aluminum electrode is immersed in pure water (hydration treatment liquid) having a temperature of 78 ° C to 92 ° C to form a hydrated film. In the chemical conversion step, the aluminum electrode is formed with a chemical conversion voltage of 400 V or higher in a chemical conversion liquid having a temperature of 58 ° C. to 78 ° C.

In such a production method, when the chemical conversion step is performed after the hydration step, the chemical conversion film is formed by both the dehydration reaction of the hydrated film and the anodizing reaction of aluminum. In the dehydration reaction of the hydrated film, the volume shrinks due to the desorption of water, so that pores (defects) occur. Some of these defects are repaired by anodizing, but they are not repaired in the absence of chemicals or water in the defects, so the unrepaired defects eventually remain in the chemical conversion film and cause leakage current. It causes an increase and a decrease in water resistance. As a result of detailed observation of the cross section of the chemical conversion film by the present inventors, it was found that the size of the defect in the chemical conversion film is several nm to several tens of nm, and it occurs particularly frequently when the chemical conversion reaches a withstand voltage of 400 V or more. rice field. It was also found that more defects occur when the liquid temperature in the hydration step is high and the chemical conversion liquid temperature is high.

More specifically, it was found that the water contained in the hydrated film was desorbed in three stages of about 60 ° C. to 90 ° C., 95 ° C. to 150 ° C., and 200 ° C. to 450 ° C. When boiling in boiling pure water as in the prior art, water is desorbed, so even when the same amount of aluminum is reacted, the amount of water in the hydrated film is reduced. Therefore, in the subsequent chemical conversion step, the water content in the chemical conversion film is insufficient and the defect cannot be sufficiently repaired. However, in the present invention, since the hydration step is performed at a relatively low temperature of 78 ° C. to 92 ° C., the water in the hydrated film is difficult to be detached, and a hydrated film having a large amount of water is formed. Therefore, since sufficient water is present in the chemical conversion film in the subsequent chemical conversion step, defects can be effectively repaired.

Further, in the chemical conversion step, the temperature of the chemical conversion liquid is changed from 58 ° C. to 78 ° C., so that it is difficult for water to be separated from the hydrated film. Therefore, since there is sufficient water in the chemical conversion film, defects can be effectively repaired.

Therefore, the number of pores exposed on the cut surface when the chemical conversion film is cut ^{can be reduced to 150 / μm 2} or less, preferably 100 / μm ² or less, so that the water resistance of the aluminum electrolytic capacitor electrode can be reduced. It is possible to improve the sex.

The defect can be removed to some extent by re-chemical formation after depolarization, but it cannot be sufficiently removed at a chemical conversion voltage of 400 V or higher. This is because the chemical conversion film is thickly formed, and even if depolarization is performed, defects inside the film are left behind. However, according to this embodiment, even if the chemical conversion film has a chemical conversion voltage of 400 V or more, defects can be reduced and the water resistance of the electrode for an aluminum electrolytic capacitor can be improved.

(Amount of hydrated film)
FIG. 3 is a graph showing an appropriate range of the amount of hydrated film produced in the hydration step in the method for manufacturing an electrode for an aluminum electrolytic capacitor to which the present invention is applied. In this embodiment, the amount of the hydrated film produced in the hydration step is the lower limit of x shown by the solid line L11 in FIG. 1 when the ratio x of the mass increased by the hydration step is expressed by the following formula (Equation 1). To the upper limit of x shown by the broken line L12 in FIG. 1.

More specifically, when the final withstand voltage of the chemical conversion film is Vf (V) and the ratio of the mass increased by the hydration step is x, the solid line L11 showing the lower limit of x is the following formula x. = (0.01 x Vf)
It is represented by. Further, the broken line L12 indicating the upper limit of x is the following formula x = (0.0117 × Vf + 28).
It is represented by.

Therefore, in this embodiment, the film withstand voltage Vf (V) and the ratio x (mass%) are the following conditional expressions (0.01 × Vf) ≦ x ≦ (0.017 × Vf + 28).
The conditions of the hydration process are set so as to satisfy the above conditions.

According to such a configuration, since the amount of the hydration film produced in the hydration step is appropriate, defects can be reduced. That is, when the amount of the hydrated film formed in the hydration step is less than the lower limit of the above conditional expression, the heat generated during chemical conversion becomes large, and it becomes difficult to proceed with the repair of defects. On the other hand, when the amount of the hydrated film formed in the hydration step is larger than the upper limit of the above conditional expression, the thickly formed hydrated film prevents the chemical conversion liquid or water from penetrating into the defect. , The repair of defects is hindered. Therefore, if the above conditions are satisfied, the number of pores exposed on the cut surface when the chemical conversion film is cut can be reduced to 150 / μm ² or less, preferably 100 / μm ² or less. The water resistance of the electrodes for electrolytic capacitors can be improved.

(Chemical process)
FIG. 4 is an explanatory diagram schematically showing a chemical conversion process of an electrode for an aluminum electrolytic capacitor to which the present invention is applied. In the chemical conversion step, for example, as shown in FIG. 4, “the aluminum electrode 10 is immersed in the chemical conversion liquid 20 stored in the chemical conversion tank (not shown). In the chemical conversion liquid 20, a pair of counter electrodes 30 are arranged. In this state, the aluminum electrode 10 is used as an anode and the counter electrode 30 is used as a negative electrode, and the aluminum electrode 10 is formed. Aluminum oxide (chemical conversion film) is formed on both sides of the aluminum electrode 10. At that time, a part of the hydrated film formed in the hydration step is dehydrated and changed to aluminum oxide, which is contained in a part of the chemical conversion film. Is done.

In such a chemical conversion step, for example, an aqueous solution of an organic acid such as adipic acid or a salt thereof is used as the chemical conversion liquid 20. For example, in an aqueous solution (organic acid-based chemical chemical solution 20) containing an organic acid such as adipic acid or a salt thereof and having a specific resistance of 5 Ωm to 500 Ωm measured at 50 ° C., the liquid temperature is 40 ° C. to 90 ° C. The aluminum electrode 10 is formed with. At that time, the voltage is increased until the power supply voltage applied between the aluminum electrode 10 and the counter electrode 30 reaches the final chemical conversion voltage Vf, and then the voltage is held at the chemical conversion voltage Vf.

Further, instead of the chemical conversion liquid 20 using an organic acid such as adipic acid or a salt thereof, an aqueous solution containing an inorganic acid such as boric acid or phosphoric acid or a salt thereof may be used as the chemical conversion liquid 20. For example, in an aqueous solution containing an inorganic acid such as boric acid or phosphoric acid or a salt thereof and having a specific resistance of 10 Ωm to 1000 Ωm measured at 90 ° C. (inorganic acid-based chemical conversion solution 20), the liquid temperature is 40 ° C to 95 ° C. Under the conditions, the aluminum electrode 10 is formed.

Further, until the final chemical conversion voltage Vf is reached, chemical conversion is carried out with a chemical conversion liquid 20 using an organic acid such as adipic acid or a salt thereof, and then chemical formation using an inorganic acid such as boric acid or phosphoric acid or a salt thereof. The liquid 20 may be used for holding at the chemical conversion voltage Vf (constant voltage chemical conversion).

Regardless of which chemical conversion liquid 20 is used, a thermal depolarization treatment for heating the aluminum electrode 10 or an in-liquid depolarization treatment for immersing the aluminum electrode 10 in an aqueous solution containing phosphate ions or the like during the chemical conversion process. Depolarization processing such as is performed. In the thermal depolarization treatment, for example, the treatment temperature is 450 ° C to 550 ° C, and the treatment time is 2 to 10 minutes. In the in-liquid depolarization treatment, the aluminum electrode 10 is immersed in an aqueous solution of 20% by mass to 30% by mass of phosphoric acid at a liquid temperature of 60 ° C. to 70 ° C. for 5 to 15 minutes depending on the film withstand voltage. do. In the submerged depolarization process, no voltage is applied to the aluminum electrode 10.

Further, a phosphoric acid immersion step of immersing the aluminum electrode 10 in an aqueous solution containing phosphoric acid ions may be performed while the voltage is increased to the chemical conversion voltage. In such a phosphoric acid dipping step, the aluminum electrode 10 is immersed in a phosphoric acid aqueous solution having a liquid temperature of 40 ° C. to 80 ° C. and a specific resistance of 0.1 Ωm to 5 Ωm measured at 60 ° C. in a time of 3 to 30 minutes. .. According to the phosphoric acid dipping step, the aluminum hydroxide precipitated in the chemical conversion step can be efficiently removed, and the subsequent production of aluminum hydroxide can be suppressed. In addition, since the phosphoric acid ion can be taken into the chemical conversion film by the phosphoric acid immersion step, the durability against immersion in boiling water or an acidic solution can be improved, and the stability of the chemical conversion film can be effectively improved. Can be improved.

(Relative velocity of chemical conversion liquid with respect to aluminum electrode)
In this embodiment, when the chemical conversion step is performed in the state shown in FIG. 2, the aluminum electrode 10 and the chemical conversion liquid 20 are in a stationary state or a moved state. To carry out chemical formation in a state where the aluminum electrode 10 is moved, the chemical formation is carried out in a state where the aluminum electrode 10 is immersed in the chemical conversion liquid 20 and is moved. To carry out chemical formation in a state where the chemical conversion liquid 20 is moved, the chemical conversion liquid 20 in which the aluminum electrode 10 is immersed is moved by circulation or stirring to carry out the chemical formation.

In this embodiment, the moving speed of the aluminum electrode 10 is represented by a three-dimensional velocity vector A, and the average flow velocity of the chemical conversion liquid 20 in the range Z0 from the surface of the aluminum electrode 10 to 10 cm in the direction perpendicular to the surface of the aluminum electrode 10. Is represented by a three-dimensional velocity vector B, the relative velocity of the chemical conversion liquid 20 with respect to the aluminum electrode 10 is represented by a three-dimensional velocity vector BA, and the absolute value of the velocity vector BA is represented by | BA |. ,
The absolute value | BA | of the velocity vector is the following conditional expression 3 cm / s ≤ | BA | ≤ 100 cm / s.
Meet.

In this embodiment, the absolute value | BA | of the velocity vector is the following conditional expression 5 cm / s ≦ | BA | ≦ 30 cm / s.
Meet.

Further, when the absolute values of the velocity vectors A and B are expressed as | A | and | B |, respectively,
The absolute values | A | and | B | of the velocity vector are the following conditional expressions 0 cm / s ≤ | A | ≤ 100 cm / s, respectively.
3 cm / s ≦ | B | ≦ 100 cm / s
Meet. Here, when the chemical formation is performed with the aluminum electrode 10 stationary, the absolute value | A | of the velocity vector becomes 0.

According to such a configuration, since the relative velocity of the chemical conversion liquid to the surface of the aluminum electrode is appropriate, the heat generated from the aluminum electrode during chemical conversion can be efficiently dissipated into the chemical conversion liquid. Therefore, it is possible to avoid a situation in which the chemical conversion film becomes hot and water is desorbed from the hydrated film more than necessary. Therefore, even if the chemical conversion voltage is 400 V or more, the defect is repaired. Therefore, the electrode for an aluminum electrolytic capacitor to which the present invention is applied has a high capacitance and few defects in the chemical conversion film, so that it is unlikely to deteriorate due to hydration. Here, when | BA | is less than 3 cm / s, the chemical conversion film cannot sufficiently dissipate heat from the surface of the aluminum electrode and the diffusion of ions becomes insufficient. It is an electrode for aluminum electrolytic capacitors that does not sufficiently repair the defects inside and has a high leakage current and is prone to hydration deterioration. On the other hand, when | BA | exceeds 100 cm / s, the capacitance tends to decrease because the elution of aluminum ions from the surface of the aluminum electrode becomes excessive.

In FIG. 2, among the directions along both surfaces of the aluminum electrode 10, the left-right direction (horizontal direction) is the X direction, and the vertical direction (vertical direction) is the Y direction. Further, the direction in which the aluminum electrode 10 and the counter electrode 30 face each other is defined as the Z direction. Therefore, the three-dimensional velocity vector A of the moving velocity of the aluminum electrode 10 corresponds to a vector obtained by synthesizing the velocity vector AX in the X direction, the velocity vector AY in the Y direction, and the velocity vector AZ in the Z direction. Further, the absolute value | A | of the velocity vector A is expressed by the following equation.
| A | = √ (AX ² + AY ² + AZ ² )

The three-dimensional velocity vector B of the moving velocity of the chemical conversion liquid 20 corresponds to a vector obtained by synthesizing the velocity vector BX in the X direction, the velocity vector BY in the Y direction, and the velocity vector BZ in the Z direction. Further, the absolute value | B | of the velocity vector B is expressed by the following equation.
| B | = √ (BX ² + BY ² + BZ ² )

The absolute value | BA | of the three-dimensional velocity vector BA | of the relative velocity of the chemical conversion liquid 20 with respect to the aluminum electrode 10 is expressed by the following equation.
| B-A | = √ ((BX-AX) ² + (BY-AY) ² + (BZ-AZ) ² )

(Example)
Next, examples and the like of the present invention will be described. Table 1 shows the manufacturing conditions of the electrodes for aluminum electrolytic capacitors according to Examples 1 and 2 of the present invention and Comparative Examples 1 and 2. Table 2 shows the characteristics of the electrodes for aluminum electrolytic capacitors according to Examples 1 and 2 of the present invention and Comparative Examples 1 and 2.

As shown in Table 1, in each of Examples 1 and 2 and Comparative Examples 1 and 2, an etched foil of high-purity aluminum surface-expanded by an etching treatment was used as the aluminum electrode. Further, at each temperature shown in Table 1, hydration treatment was performed in pure water so that the ratio of the mass of the hydration film formed by the hydration step to the mass of the aluminum electrode before the boiling step was 20%. After that, chemical conversion was carried out with each type of chemical conversion liquid shown in Table 1. At that time, in the chemical conversion step, the phosphoric acid aqueous solution was immersed and the depolarization treatment was performed by heat treatment. The chemical conversion voltage is 600V. Further, the absolute value | BA | of the three-dimensional velocity vector BA | of the relative velocity of the chemical conversion liquid with respect to the aluminum electrode was set to 10 cm / s.

Next, the hydration resistance of the aluminum electrode was measured. Measurement of water resistance is EIAJ
It is a result of measurement according to "Test method of electrode foil for aluminum electrolytic capacitor" specified in RC 2364A. For example, the hydration resistance is obtained by immersing in pure water at 95 ° C. or higher for 60 ± 1 minutes and then applying a constant current. It is shown by the time (seconds) until the film is boosted to the withstand voltage. In addition, the cross section of the chemical conversion film was observed by FE-SEM and image analysis was performed to measure the number of defects ^{in the chemical conversion film 1 μm 2.}

In Examples 1 and 2, since the temperature of the hydration step and the temperature of the chemical conversion liquid are appropriate, the hydration resistance is good. In Comparative Example 1, the temperature of the hydration step is appropriate, but the temperature of the chemical conversion liquid is high, so that dehydration from the hydrated film increases. As a result, a chemical conversion film having many defects is formed, resulting in poor hydration resistance. In Comparative Example 2, the temperature of the chemical conversion liquid is appropriate, but the temperature of the hydration step is high, so that the water content in the hydrated film is reduced. As a result, a chemical conversion film having many defects is formed, resulting in poor hydration resistance.

(Other embodiments)
In the above embodiment, an etched foil is used as the aluminum electrode, but the same applies when a porous aluminum electrode or the like in which a porous layer formed by sintering aluminum powder is laminated on both sides of an aluminum core material is used. Results have been obtained. Further, as a result of examining various conditions other than the above-mentioned examples, if the above-mentioned conditions are satisfied, the result is that defects in the chemical conversion film can be reduced even if the chemical conversion film has a chemical conversion voltage of 400 V or more. Has been obtained.

10 ... Aluminum electrode, 20 ... Chemical solution, 30 ... Counter electrode

Claims (7)

An electrode for an aluminum electrolytic capacitor in which a chemical conversion film having a withstand voltage of 400 V or more is formed on an aluminum electrode.
The number of pores existing inside the chemical conversion film exposed on the cut surface when the chemical conversion film is cut is 150 / μm ² or less.
An electrode for an aluminum electrolytic capacitor, characterized in that the size of the pores is several nm to several tens of nm. An electrode for an aluminum electrolytic capacitor in which a chemical conversion film having a withstand voltage of 400 V or more is formed on an aluminum electrode.
When the cut surface when the chemical conversion film is cut is observed by FE-SEM, the number of pores existing inside the chemical conversion film exposed on the cut surface is 150 / μm ² or less. Electrodes for aluminum electrolytic capacitors. The electrode for an aluminum electrolytic capacitor according to claim 1 or 2, wherein the number of pores is 100 / μm ^{2 or less.} The electrode for an aluminum electrolytic capacitor according to any one of claims 1 to 3, wherein the aluminum electrode is made of an etched foil obtained by etching an aluminum foil. The feature is that the number of pores existing inside the chemical conversion film exposed on the cut surface when the chemical conversion film is cut so as to cross the tunnel-shaped pit generated by etching is 150 / μm ^{2 or less.} 4. The electrode for an aluminum electrolytic capacitor according to claim 4. The aluminum electrolytic capacitor according to any one of claims 1 to 3, wherein the aluminum electrode is a porous aluminum electrode on which a porous layer made by sintering aluminum powder is laminated. electrode. Claim 6, wherein the number of pores present in the conversion coating inner exposed at the cut surface upon cutting the conversion coating to traverse the porous layer is 150 / [mu] m ² or less Electrodes for aluminum electrolytic capacitors as described in.

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